'use strict';

function double_to_one(collection) {
  let arr = [] ;
  for(let array of collection){
    arr = arr.concat(array);
  }
  return [...new Set(arr)] ;
  //在这里写入代码
}

module.exports = double_to_one;
// var collection = [[1, 2, 3], [5, 2, 1, 4], [2, 1]];
// console.log(double_to_one(collection));